MEXICO CITY, Sept 12 (Reuters) - Mexican state oil company Pemex said on Thursday it had placed $7.5 billion worth of bonds with maturities of seven, 10 and 30 years that will be used for debt refinancing.

The placement was more than five times oversubscribed, with total demand reaching $38 billion, Pemex said in a statement.

Pemex, formally known as Petroleos Mexicanos, said the transaction is the biggest in its history. (Reporting by Ana Isabel Martinez Editing by Dave Graham)